Stimulation of anatomical regions of a patient is a clinical technique for the treatment of disorders. Such stimulation can include deep brain stimulation (DBS), spinal cord stimulation (SCS), Occipital NS therapy, Trigemenal NS therapy, Vagus NS therapy, peripheral field stimulation therapy, sacral root stimulation therapy, or other such therapies. For example, DBS may include stimulation of the thalamus or basal ganglia and may be used to treat disorders such as essential tremor, Parkinson's disease (PD), and other physiological disorders, including psychiatric disorders. DBS may also be useful for traumatic brain injury and stroke. Pilot studies have also begun to examine the utility of DBS for treating dystonia, epilepsy, and obsessive-compulsive disorder.
However, understanding of the therapeutic mechanisms of action remains elusive. The stimulation parameters, electrode geometries, or electrode locations that are best suited for existing or future uses of DBS also are unclear.
For conducting a therapeutic stimulation, a neurosurgeon can select a target region within the patient anatomy, e.g., within the brain for DBS, an entry point, e.g., on the patient's skull, and a desired trajectory between the entry point and the target region. The entry point and trajectory are typically carefully selected to avoid intersecting or otherwise damaging certain nearby critical structures or vasculature. A stimulation electrode leadwire used to provide the stimulation to the relevant anatomical region is inserted along the trajectory from the entry point toward the target region. The stimulation electrode leadwire typically includes multiple closely-spaced electrically independent stimulation electrode contacts.
The target anatomical region can include tissue that exhibit high electrical conductivity. For a given stimulation parameter setting, a respective subset of the fibers are responsively activated. A stimulation parameter can include a current amplitude or voltage amplitude, which may be the same for all of the electrodes of the leadwire, or which may vary between different electrodes of the leadwire. The applied amplitude setting results in a corresponding current in the surrounding fibers, and therefore a corresponding voltage distribution in the surrounding tissue. The complexity of the inhomogeneous and anisotropic fibers makes it difficult to predict the particular volume of tissue influenced by the applied stimulation.
A treating physician typically would like to tailor the stimulation parameters (such as which one or more of the stimulating electrode contacts to use, the stimulation pulse amplitude, e.g., current or voltage depending on the stimulator being used, the stimulation pulse width, and/or the stimulation frequency) for a particular patient to improve the effectiveness of the therapy. Parameter selections for the stimulation can be achieved via tedious and variable trial-and-error, without visual aids of the electrode location in the tissue medium or computational models of the volume of tissue influenced by the stimulation. Such a method of parameter selection is difficult and time-consuming and, therefore, expensive. Moreover, it may not necessarily result in the best possible therapy.
Systems have been proposed that provide an interface that facilitates parameter selections. See, for example, U.S. patent application Ser. No. 12/454,330, filed May 15, 2009 (“the '330 application”), U.S. patent application Ser. No. 12/454,312, filed May 15, 2009 (“the '312 application”), U.S. patent application Ser. No. 12/454,340, filed May 15, 2009 (“the '340 application”), U.S. patent application Ser. No. 12/454,343, filed May 15, 2009 (“the '343 application”), and U.S. patent application Ser. No. 12/454,314, filed May 15, 2009 (“the '314 application”), the content of each of which is hereby incorporated herein by reference in its entirety.
The leadwire can include cylindrically symmetrical electrodes, which, when operational, produce approximately the same electric values in all positions at a similar distance from the electrode in any plane that cuts through the electrode. Alternatively, the leadwire can include directional electrodes that produce different electrical values depending on the direction from the electrode. For example, the leadwire can include multiple separately controllable electrodes arranged cylindrically about the leadwire at each of a plurality of levels of the leadwire. Each electrode may be set as an anode or cathode in a bipolar configuration or as a cathode, with, for example, the stimulator casing being used as ground, in a monopolar arrangement.
When programming a leadwire for tissue stimulation, e.g., DBS, the clinical standard of care is often to perform a monopolar review (MPR) upon activation of the leadwire in order to determine the efficacy and side-effect thresholds for all electrodes on the leadwire, on an electrode-by-electrode basis. Monopolar review, rather than bipolar review, is performed because monopolar stimulation often requires a lower stimulation intensity than bipolar stimulation to achieve the same clinical benefit. The MPR can inform the selection of a first clinical program (parameters for stimulation) for treating a patient.
Such systems for programming a leadwire for tissue stimulation display a graphical representation of an area within which it is estimated that there is or could be tissue activation, referred to herein as a volume of activation (VOA), that results from input stimulation parameters. For example, the VOA can be calculated as a region outside of which stimulation is estimated to be unlikely. The VOA can be displayed relative to an image or model of a portion of the patient's anatomy.
Generation of the VOA may be based on Neural Element Models such as a model of fibers, e.g., axons, and a voltage distribution about the leadwire and on detailed processing thereof. Performing such processing to provide a VOA preview in real-time response to a clinician's input of parameters is not practical because of the significant required processing time. Therefore, conventional systems pre-process various stimulation parameter settings to determine which axons are activated by the respective settings.
Those systems also provide interfaces via which to input selections of the stimulation parameters and notes concerning therapeutic and/or side effects of stimulations associated with graphically represented VOAs.